1. Field of the Invention
The present invention is directed to a connection fitting in an internal combustion engine for connecting a high voltage ignition cable with the terminal fittings of a spark plug or a distributor.
2. Related Art
A conventional spark plug cap for an internal combustion engine comprises a connection fitting and an ignition cable secured together and covered by an insulator. A high voltage current is supplied to the spark plug through the ignition cable.
As shown in FIG. 7, a conventional spark plug cap 100 for a double overhead cam (DOHC) engine is long and slender and connects an ignition cable 101 with an spark plug 3 attached to the bottom portion of a spark plug attaching hole 2.
The ignition cable 101 is connected to a discharge tube 103 by a crimping connector 102 or other connecting means, and a contact spring 104 is interposed between the discharge tube 103 and a connection fitting 105 which engages a terminal 3a of the spark plug 3. These parts are covered by a substantially cylindrical insulator 107 molded from insulating rubber or resin so that the parts are insulated and protected.
An end cap 108 made of insulating material is engaged with an end of the insulator 107. An inner circumferential wall of the end cap 108 engages an insulating portion 3b of the spark plug 3, and a gap is formed between the outer circumferential surface of the end cap 108 and the inner circumferential wall of the spark plug attaching hole 2 so that the outer circumferential surface of the end cap 108 does not contact the internal circumferential wall of the spark plug attaching hole 2. The plug cap 100 is thus easily inserted into the spark plug attaching hole 2, and the spark plug 3 is enclosed in an airtight fashion for improved insulation.
At an end of the insulator 107 opposite the spark plug 3, a rain cap 109 is provided and engaged in an opening portion of the spark plug attaching hole 2. The rain cap 109 prevents water and dust from entering the spark plug attaching hole 2.
In the plug cap 200 shown in FIG. 8, an ignition cable 201 is directly connected with the spark plug 3 by a crimping connector 203. Otherwise, the plug cap 200 is substantially the same as the plug cap 100 in FIG. 7.
FIG. 9 is a partial cross sectional view showing a connection cap 300 for connecting an ignition cable 301 with a terminal fitting 6 provided at a bottom portion of an ignition cable attaching hole 5 of a distributor 4. The connection cap 300 includes an L-shaped cylindrical connection fitting 302, one end of which is connected with the ignition cable 301 and the other end of which is engaged with the terminal fitting 6, as well as an insulator 303 made of insulating rubber which covers the connection fitting 302. The insulator 303 is engaged with the ignition cable attaching hole 5 so that the terminal fitting 6 is enclosed and insulated in an airtight fashion.
In the aforementioned plug caps 100, 200, the connection fittings 105, 203 are integrally molded with the insulators 107, 207. Locking means 114, 124 respectively provided in the connection fittings 105, 203 are engaged with the terminal fitting 3a of the spark plug 3. Further, the rain caps 109, 209 are engaged in the opening of the spark plug attaching hole 2.
Likewise, in the distributor connection cap 300 shown in FIG. 9, the connection fitting 302 is integrally molded with the insulator 303, and the insulator 303 is engaged with the ignition cable attaching hole 5.
In some instances, due to poor manufacturing tolerances, the axes of the insulators 107, 207, 303 are eccentric with respect to the axes of the connection fittings 105,203,302. Also, the axis of the spark plug attaching hole 2 may be eccentric with respect to the axis of the spark plug 3. Likewise, the axis of the ignition cable attaching hole 5 may be eccentric with respect to the axis of the terminal fitting 6.
The connection fittings 105, 203 are press fitted on the terminal fitting 3a of the spark plug 3, and the rain caps 109, 209 are press fitted in the spark plug attaching hole 2. Likewise, the connection fitting 302 is press fitted in the terminal fitting 6, and the insulator 303 is press fitted in the ignition cable attaching hole 5.
Accordingly, when the automobile engine vibrates and the spark plugs and distributor are assembled as described above, the connection fittings 105, 203, 303, the spark plug 3, and the terminal fitting 6 are caused to be in frictional contact and, over time, they may become loose or even disengaged.
The rain caps 109, 209 gradually deteriorate due to the heat generated from the engine, and the insulator 303 may be deformed over time, so that the plug caps and the insulator may become disengaged from the spark plug attaching hole 2 and the ignition cable attaching hole 5, respectively. The plug caps 100, 200 and the distributor connection cap 300 may therefore vibrate differently from the engine, increasing frictional abrasion. This is particularly true for the plug cap 100 shown in FIG. 7 since the weight of the plug cap 100 is disproportionately high at the discharge tube 103, i.e., a large inertial force is generated at the discharge tube 103 when the plug cap 100 is vibrated.
Accordingly, an object of the present invention is to prevent the frictional abrasion of connection fittings and terminal fittings which occur in the conventional ignition cable connection fittings described above.